The proposed research is an outgrowth of our earlier studies in which we demonstrated intracellular prolactin binding sites in rat ventral, dorsal and lateral prostate, rat R3327 prostatic carcinoma and normal and abnormal human prostate. We developed an immunohistochemical in vitro assay in which tissue sections were exposed to purified NIAMDD prolactin prior to an immunoperoxidase staining sequence. In the course of these innunohistochemical studies we also found human placental lactogen (HPL) immunoreactivity in rat pituitary gland. We propose to continue development of the in vitro immunohistochemical assay for prolactin binding sites in both rat and human prostate tissue with particular emphasis being placed on establishing biological specificity, quantification of the assay and ultrastructural localization. Immunohistochemistry will also be used to determine whether prolactin enters rat prostate epithelial cells in vivo and whether the binding of prolactin in vivo is androgen dependent. Tissues from these in vivo experiments will be examined morphologically and histochemically (specific prostate markers and steroid receptors) to define the primary physiological effects of prolactin and of the prolactin androgen interplay on the prostate. In other experiments we intend to examine prolactin binding, its regulation and the physiological role of the hormone in R3327 rat prostatic tumors. We also hope to determine whether and HPL-like peptide is secreted by the rat pituitary and, if so, whether this peptide is involved in prostatic function. This work will hopefully add insight to understanding the mechanisms of prolactin action and the prolactin-androgen interplay and define the primary lactogenic hormone effects in normal and abnormal prostate.